1. Field of the Invention
The invention relates to a process for the preparation of ethynylcyclopropane of the formula: ##STR1##
Ethynylcyclopropane is an intermediate in the synthesis of pharmaceutically active ingredients, for example, antiviral agents for combating HIV infections (international Published Patent Application No. WO 96/22955).
2. Background Art
A known synthesis of ethynylcyclopropane starts from 1-bromo-3-chloropropane, which is reacted with sodium acetylide to give 5-chloro-1-pentyne. The latter compound is cyclized with n-butyllrthium to give the desired compound. A disadvantage of such process is that it requires low temperatures. Another known process starts from cyclopropyl methyl ketone, which is first converted into (1,1-dichloroethyl)cyclopropane. The desired product is obtained from the latter compound by eliminating two molecules of hydrogen chloride. It is a disadvantage of such process that the preparation of the geminal dichloride requires drastic conditions (e.g., PCl.sub.5). In addition, both of the prior art processes mentioned produce at least 2 mols of halide waste per mole of product.